Active material actuator assembly

ABSTRACT

Active material actuator assemblies are provided that enable simplified control systems and faster actuator cycle times. A movable member is provided that has multiple active material components operatively connected to it. The active material components are separately selectively activatable for moving the movable member. Movement of the movable member via activation of a first of the active material components triggers activation of the second active material component to further move the movable member. Alternatively or in addition, previously activated active material components are protected from undesired stretching during activation of another active material component or, when desired, an active material component may be reset via activation of another of the active material components in order to prepare it for subsequent activation.

TECHNICAL FIELD

The invention relates to active material actuator assemblies.

BACKGROUND OF THE INVENTION

Active materials include those compositions that can exhibit a change instiffness properties, shape and/or dimensions in response to anactivation signal, which can be an electrical, magnetic, thermal or alike field depending on the different types of active materials.Preferred active materials include but are not limited to the class ofshape memory materials, and combinations thereof. Shape memorymaterials, a class of active materials, also sometimes referred to assmart materials, refer to materials or compositions that have theability to remember their original shape, which can subsequently berecalled by applying an external stimulus (i.e., an activation signal).As such, deformation of the shape memory material from the originalshape can be a temporary condition.

SUMMARY OF THE INVENTION

Active material actuator assemblies are provided that enable simplifiedcontrol systems and faster actuation cycle times. In one aspect of theinvention, a movable member is provided that has multiple activematerial components operatively connected to it. The active materialcomponents are separately selectively activatable to actuate and therebymove the movable member. Movement of the movable member via activationof a first of the active material components triggers activation of thesecond active material component to further move the movable member. Theactivation may be accomplished via activation mechanisms, such aselectrical contact strips, that are positioned so that an electricalcircuit that activates the second active material component is completedby movement of the movable member in response to the activation of thefirst active material component. In the case of fluid heating, flowredirecting mechanisms such as spool valves can be arranged so thatactuation of the first movable member moves a spool valve to completeanother fluid circuit and thereby trigger activation of the secondactive material component to further move the movable member. Becauseactivation of the second active material component is physically linkedto movement of the movable member via the first active materialcomponent, control system algorithms to activate the second activematerial component are not necessary, potentially reducing costs.

In another aspect of the invention, multiple active material componentsoperatively connected to a movable member are each separatelyselectively activatable in repeating series for sequential actuation formoving the movable member and are configured such that a previouslyactivated one of said active material components is not reset (e.g.,stretched) by actuation of a currently activated active materialcomponent. Accordingly, the previously activated component is given timeto reduce its resistance to resetting (e.g., to cool) before it is resetand reactivated and thus does not provide resistance during actuation ofthe currently activated component, increasing efficiency of the actuatorassembly.

In another aspect of the invention, multiple active material componentsoperatively connected to a movable member are each separatelyselectively activatable in repeating series for moving the movablemember and are configured such that a subsequently activated one of saidactive material components is at least partially reset by actuation of acurrently activated one of said active material components. When it istime for the subsequently activated active material component to beactivated, it has been wholly reset by one or more of the previouslyactivated active material components to its preactivation state (e.g., amartensite phase in an SMA) in preparation for activation. This“resetting” is physically accomplished via actuation of at least oneactive material component and therefore additional control systemalgorithms to reset the active material components are not necessary,potentially reducing costs. Additionally, because the resetting ismechanically accomplished, resetting may be more exact than oneaccomplished via a control system relying on feedback with itsassociated inaccuracies.

The active material actuator assemblies provided herein may function asrotational motors that are more efficient than previous stepping motorsthat use four shape memory coil springs pulling a biased pin from fourdifferent directions to achieve rotation by actuating the SMA springssequentially. In known stepping motors, only a relatively small force isapplied by the springs. Additionally, in such designs after contractionof a spring, it is still relatively hot compared to the ambienttemperature and will apply large resistance to the pulling by the nextspring compared to the resistance it applies when its temperature isclose to ambient (i.e., when in the martensite phase). Finally, there isa waste of the amount of stretch each spring is subjected to since eachspring is overstretched by the opposite one and only part of the stretchis used to pull the pin and turn the shaft. The cooperative resistancereduction and resetting mechanism in the rotational motors proposed herecan also be used to avoid overstretch such that the full amount ofstretch an active material component is subject to is used to do usefulwork and rotate the shaft.

The above features and advantages and other features and advantages ofthe present invention are readily apparent from the following detaileddescription of the best modes for carrying out the invention when takenin connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic, partially cross-sectional illustration of a firstembodiment of a telescoping active material actuator assembly;

FIG. 2 is a graph of load displacement versus time for the activematerial actuator assembly of FIG. 1;

FIG. 3 is a graph of load holding force versus time for the activematerial actuator assembly of FIG. 1;

FIG. 4 is a schematic, partially cross-sectional illustration of asecond embodiment of a telescoping active material actuator assemblywith movable members having bellows;

FIG. 5 is a schematic, partially cross-sectional illustration inpartially fragmentary view of a third embodiment of a telescoping activematerial actuator assembly having automatic sequential activation;

FIG. 6 is a schematic illustration of an exemplary embodiment of alocking mechanism for use on any of the actuator assemblies of FIGS. 1,4 and 5;

FIG. 7 is a schematic perspective illustration of a fourth embodiment ofan active material actuator assembly;

FIG. 8 is a schematic perspective illustration in cross-sectional viewof the actuator assembly of FIG. 7;

FIG. 9 is a schematic fragmentary, cross-sectional view of the actuatorassembly of FIGS. 7 and 8 with some of the active material componentsactivated and the movable members locked together;

FIG. 10 is a schematic perspective illustration of another embodiment ofan active material actuator assembly;

FIG. 11 is a schematic rear view illustration of the active materialactuator assembly of FIG. 10;

FIG. 12 is a schematic illustration in fragmentary, partially rotatedview of the cam lobe and pulleys of FIGS. 10 and 11 taken along thearrows shown in FIG. 11;

FIG. 13 is a schematic end view illustration of another embodiment of anactive material actuator assembly; and

FIG. 14 is a schematic perspective illustration of the active materialactuator assembly of FIG. 13 showing an opposing end.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A number of exemplary embodiments of active material actuator assemblieswithin the scope of the invention are described herein. The activematerial actuator assemblies all utilize active material components thatmay be, but are not limited to, a class of active materials called shapememory materials. Exemplary shape memory materials include shape memoryalloys (SMAs), electroactive polymers (EAPs) such as dielectricelastomers, ionic polymer metal composites (IPMC), piezoelectricpolymers and shape memory polymers (SMPs), magnetic shape memory alloys(MSMA), shape memory ceramics (SMCs), baroplastics, piezoelectricceramics, magnetorheological (MR) elastomers, composites of theforegoing shape memory materials with non-shape memory materials, andcombinations comprising at least one of the foregoing shape memorymaterials. For convenience and by way of example, reference herein willbe made to shape memory alloys and shape memory polymers. The shapememory ceramics, baroplastics, and the like can be employed in a similarmanner as will be appreciated by those skilled in the art in view ofthis disclosure. For example, with baroplastic materials, a pressureinduced mixing of nanophase domains of high and low glass transitiontemperature (Tg) components effects the shape change. Baroplastics canbe processed at relatively low temperatures repeatedly withoutdegradation. SMCs are similar to SMAs but can tolerate much higheroperating temperatures than can other shape-memory materials. An exampleof an SMC is a piezoelectric material.

The ability of shape memory materials to return to their original shapeupon the application of external stimuli has led to their use inactuators to apply force resulting in desired motion. Smart materialactuators offer the potential for a reduction in actuator size, weight,volume, cost, noise and an increase in robustness in comparison withtraditional electromechanical and hydraulic means of actuation. However,most active materials are capable of providing only limiteddisplacement, limiting their use in applications requiring a largedisplacement, whether linear or rotational. The invention describedherein solves this problem.

SMAs

Shape memory alloys are alloy compositions with at least two differenttemperature-dependent phases. The most commonly utilized of these phasesare the so-called martensite and austenite phases. In the followingdiscussion, the martensite phase generally refers to the moredeformable, lower temperature phase whereas the austenite phasegenerally refers to the more rigid, higher temperature phase. When theshape memory alloy is in the martensite phase and is heated, it beginsto change into the austenite phase. The temperature at which thisphenomenon starts is often referred to as austenite start temperature(A_(s)). The temperature at which this phenomenon is complete is oftencalled the austenite finish temperature (A_(f)). When the shape memoryalloy is in the austenite phase and is cooled, it begins to change intothe martensite phase, and the temperature at which this phenomenonstarts is often referred to as the martensite start temperature (M_(s)).The temperature at which austenite finishes transforming to martensiteis often called the martensite finish temperature (M_(f)). The rangebetween A_(s) and A_(f) is often referred to as themartensite-to-austenite transformation temperature range while thatbetween M_(s) and M_(f) is often called the austenite-to-martensitetransformation temperature range. It should be noted that theabove-mentioned transition temperatures are functions of the stressexperienced by the SMA sample. Generally, these temperatures increasewith increasing stress. In view of the foregoing properties, deformationof the shape memory alloy is preferably at or below the austenite starttemperature (at or below A_(s)). Subsequent heating above the austenitestart temperature causes the deformed shape memory material sample tobegin to revert back to its original (nonstressed) permanent shape untilcompletion at the austenite finish temperature. Thus, a suitableactivation input or signal for use with shape memory alloys is a thermalactivation signal having a magnitude that is sufficient to causetransformations between the martensite and austenite phases.

The temperature at which the shape memory alloy remembers its hightemperature form (i.e., its original, nonstressed shape) when heated canbe adjusted by slight changes in the composition of the alloy andthrough thermo-mechanical processing. In nickel-titanium shape memoryalloys, for example, it can be changed from above about 100 degreesCelsius to below about −100 degrees Celsius. The shape recovery processcan occur over a range of just a few degrees or exhibit a more gradualrecovery over a wider temperature range. The start or finish of thetransformation can be controlled to within several degrees depending onthe desired application and alloy composition. The mechanical propertiesof the shape memory alloy vary greatly over the temperature rangespanning their transformation, typically providing shape memory effectand superelastic effect. For example, in the martensite phase a lowerelastic modulus than in the austenite phase is observed. Shape memoryalloys in the martensite phase can undergo large deformations byrealigning the crystal structure arrangement with the applied stress. Aswill be described in greater detail below, the material will retain thisshape after the stress is removed.

Suitable shape memory alloy materials include, but are not intended tobe limited to, nickel-titanium based alloys, indium-titanium basedalloys, nickel-aluminum based alloys, nickel-gallium based alloys,copper based alloys (e.g., copper-zinc alloys, copper-aluminum alloys,copper-gold, and copper-tin alloys), gold-cadmium based alloys,silver-cadmium based alloys, indium-cadmium based alloys,manganese-copper based alloys, iron-platinum based alloys,iron-palladium based alloys, and the like. The alloys can be binary,ternary, or any higher order so long as the alloy composition exhibits ashape memory effect, e.g., change in shape, orientation, yield strength,flexural modulus, damping capacity, superelasticity, and/or similarproperties. Selection of a suitable shape memory alloy compositiondepends, in part, on the temperature range of the intended application.

The recovery to the austenite phase at a higher temperature isaccompanied by very large (compared to that needed to deform thematerial) stresses which can be as high as the inherent yield strengthof the austenite material, sometimes up to three or more times that ofthe deformed martensite phase. For applications that require a largenumber of operating cycles, a strain in the range of up to 4% or more ofthe deformed length of wire used can be obtained. In experimentsperformed with Flexinol® wires of 0.5 mm diameter, the maximum strain inthe order of 4% was obtained. This percentage can increase up to 8% forthinner wires or for applications with a low number of cycles. Thislimit in the obtainable strain places significant constraints in theapplication of SMA actuators where space is limited.

SMPs

As previously mentioned, other suitable shape memory materials are shapememory polymers (SMPs). “Shape memory polymer” generally refers to apolymeric material, which exhibits a change in a property, such as ashape, a dimension, a shape orientation, or a combination comprising atleast one of the foregoing properties in combination with a change inits elastic modulus upon application of an activation signal. Shapememory polymers may be thermoresponsive (i.e., the change in theproperty is caused by a thermal activation signal), photoresponsive(i.e., the change in the property is caused by a light-based activationsignal), moisture-responsive (i.e., the change in the property is causedby a liquid activation signal such as humidity, water vapor, or water),or a combination comprising at least one of the foregoing.

Generally, SMPs are phase segregated co-polymers comprising at least twodifferent units, which may be described as defining different segmentswithin the SMP, each segment contributing differently to the overallproperties of the SMP. As used herein, the term “segment” refers to ablock, graft, or sequence of the same or similar monomer or oligomerunits, which are copolymerized to form the SMP. Each segment may becrystalline or amorphous and will have a corresponding melting point orglass transition temperature (T_(g)), respectively. The term “thermaltransition temperature” is used herein for convenience to genericallyrefer to either a Tg or a melting point depending on whether the segmentis an amorphous segment or a crystalline segment. For SMPs comprising(n) segments, the SMP is said to have a hard segment and (n-1) softsegments, wherein the hard segment has a higher thermal transitiontemperature than any soft segment. Thus, the SMP has (n) thermaltransition temperatures. The thermal transition temperature of the hardsegment is termed the “last transition temperature”, and the lowestthermal transition temperature of the so-called “softest” segment istermed the “first transition temperature”. It is important to note thatif the SMP has multiple segments characterized by the same thermaltransition temperature, which is also the last transition temperature,then the SMP is said to have multiple hard segments.

When the SMP is heated above the last transition temperature, the SMPmaterial can be imparted a permanent shape. A permanent shape for theSMP can be set or memorized by subsequently cooling the SMP below thattemperature. As used herein, the terms “original shape”, “previouslydefined shape”, “predetermined shape”, and “permanent shape” aresynonymous and are intended to be used interchangeably. A temporaryshape can be set by heating the material to a temperature higher than athermal transition temperature of any soft segment yet below the lasttransition temperature, applying an external stress or load to deformthe SMP, and then cooling below the particular thermal transitiontemperature of the soft segment while maintaining the deforming externalstress or load.

The permanent shape can be recovered by heating the material, with thestress or load removed, above the particular thermal transitiontemperature of the soft segment yet below the last transitiontemperature. Thus, it should be clear that by combining multiple softsegments it is possible to demonstrate multiple temporary shapes andwith multiple hard segments it may be possible to demonstrate multiplepermanent shapes. Similarly using a layered or composite approach, acombination of multiple SMPs will demonstrate transitions betweenmultiple temporary and permanent shapes.

EAPS

The active material may also comprise an electroactive polymer such asionic polymer metal composites, conductive polymers, piezoelectricpolymeric material and the like. As used herein, the term“piezoelectric” is used to describe a material that mechanically deformswhen a voltage potential is applied, or conversely, generates anelectrical charge when mechanically deformed

Electroactive polymers include those polymeric materials that exhibitpiezoelectric, pyroelectric, or electrostrictive properties in responseto electrical or mechanical fields. The materials generally employ theuse of compliant electrodes that enable polymer films to expand orcontract in the in-plane directions in response to applied electricfields or mechanical stresses. An example of an electrostrictive-graftedelastomer is a piezoelectric poly (vinyldenefluoride-trifluoro-ethylene) copolymer. This combination has the abilityto produce a varied amount of ferroelectric-electrostrictive molecularcomposite systems. These may be operated as a piezoelectric sensor oreven an electrostrictive actuator.

Materials suitable for use as an electroactive polymer may include anysubstantially insulating polymer or rubber (or combination thereof) thatdeforms in response to an electrostatic force or whose deformationresults in a change in electric field. Exemplary materials suitable foruse as a pre-strained polymer include silicone elastomers, acrylicelastomers, polyurethanes, thermoplastic elastomers, copolymerscomprising PVDF, pressure-sensitive adhesives, fluoroelastomers,polymers comprising silicone and acrylic moieties, and the like.Polymers comprising silicone and acrylic moieties may include copolymerscomprising silicone and acrylic moieties, polymer blends comprising asilicone elastomer and an acrylic elastomer, for example.

Materials used for electrodes of the present disclosure may vary.Suitable materials used in an electrode may include graphite, carbonblack, colloidal suspension, thin metals including silver and gold,silver filled and carbon filled gels and polymers, and ionically orelectronically conductive polymers. It is understood that certainelectrode materials may work well with particular polymers and may notwork as well for others. By way of example, carbon fibrils work wellwith acrylic elastomer polymers while not as well with siliconepolymers.

SMCs/Piezoelectric

The active material may also comprise a piezoelectric material. Also, incertain embodiments, the piezoelectric material may be configured as anactuator for providing rapid deployment. As used herein, the term“piezoelectric” is used to describe a material that mechanically deforms(changes shape) when a voltage potential is applied, or conversely,generates an electrical charge when mechanically deformed. Preferably, apiezoelectric material is disposed on strips of a flexible metal orceramic sheet. The strips can be unimorph or bimorph. Preferably, thestrips are bimorph, because bimorphs generally exhibit more displacementthan unimorphs.

One type of unimorph is a structure composed of a single piezoelectricelement externally bonded to a flexible metal foil or strip, which isstimulated by the piezoelectric element when activated with a changingvoltage and results in an axial buckling or deflection as it opposes themovement of the piezoelectric element. The actuator movement for aunimorph can be by contraction or expansion. Unimorphs can exhibit astrain of as high as about 10%, but generally can only sustain low loadsrelative to the overall dimensions of the unimorph structure. Acommercial example of a pre-stressed unimorph is referred to as“THUNDER”, which is an acronym for Thin layer composite UNimorphferroelectric Driver and sEnsoR. THUNDER is a composite structureconstructed with a piezoelectric ceramic layer (for example, leadzirconate titanate), which is electroplated on its two major faces. Ametal pre-stress layer is adhered to the electroplated surface on atleast one side of the ceramic layer by an adhesive layer (for example,“LaRC-SI®” developed by the National Aeronautics and SpaceAdministration (NASA)). During manufacture of a THUNDER actuator, theceramic layer, the adhesive layer, and the first pre-stress layer aresimultaneously heated to a temperature above the melting point of theadhesive, and then subsequently allowed to cool, thereby re-solidifyingand setting the adhesive layer. During the cooling process the ceramiclayer becomes strained, due to the higher coefficients of thermalcontraction of the metal pre-stress layer and the adhesive layer than ofthe ceramic layer. Also, due to the greater thermal contraction of thelaminate materials than the ceramic layer, the ceramic layer deformsinto an arcuate shape having a generally concave face.

In contrast to the unimorph piezoelectric device, a bimorph deviceincludes an intermediate flexible metal foil sandwiched between twopiezoelectric elements. Bimorphs exhibit more displacement thanunimorphs because under the applied voltage one ceramic element willcontract while the other expands. Bimorphs can exhibit strains up toabout 20%, but similar to unimorphs, generally cannot sustain high loadsrelative to the overall dimensions of the unimorph structure.

Suitable piezoelectric materials include inorganic compounds, organiccompounds, and metals. With regard to organic materials, all of thepolymeric materials with noncentrosymmetric structure and large dipolemoment group(s) on the main chain or on the side-chain, or on bothchains within the molecules, can be used as candidates for thepiezoelectric film. Examples of suitable polymers include, for example,but are not limited to, poly(sodium 4-styrenesulfonate) (“PSS”), polyS-119 (Poly(vinylamine) backbone azo chromophore), and theirderivatives; polyfluorocarbines, including polyvinylidene fluoride(“PVDF”), its co-polymer vinylidene fluoride (“VDF”), trifluorethylene(TrFE), and their derivatives; polychlorocarbons, includingpoly(vinylchloride) (“PVC”), polyvinylidene chloride (“PVC2”), and theirderivatives; polyacrylonitriles (“PAN”), and their derivatives;polycarboxylic acids, including poly (metharcylic acid (“PMA”), andtheir derivatives; polyureas, and their derivatives; polyerethanes(“PUE”), and their derivatives; bio-polymer molecules such aspoly-L-lactic acids and their derivatives, and membrane proteins, aswell as phosphate bio-molecules; polyanilines and their derivatives, andall of the derivatives of tetramines; polyimides, including Kaptonmolecules and polyetherimide (“PEI”), and their derivatives; all of themembrane polymers; poly (N-vinyl pyrrolidone) (“PVP”) homopolymer, andits derivatives, and random PVP-co-vinyl acetate (“PVAc”) copolymers;and all of the aromatic polymers with dipole moment groups in themain-chain or side-chains, or in both the main-chain and theside-chains, and mixtures thereof.

Further, piezoelectric materials can include Pt, Pd, Ni, T, Cr, Fe, Ag,Au, Cu, and metal alloys and mixtures thereof. These piezoelectricmaterials can also include, for example, metal oxide such as SiO₂,Al₂O₃, ZrO₂, TiO₂, SrTiO₃, PbTiO₃, BaTiO₃, FeO₃, Fe₃O₄, ZnO, andmixtures thereof; and Group VIA and IIB compounds, such as CdSe, CdS,GaAs, AgCaSe₂, ZnSe, GaP, InP, ZnS and mixtures thereof.

MR Elastomers

Suitable active materials also comprise magnetorheological (MR)compositions, such as MR elastomers, a class of smart materials whoserheological properties can rapidly change upon application of a magneticfiled. MR elastomers are suspensions of micrometer-sized, magneticallypolarizable particles in a thermoset elastic polymer or rubber. Thestiffness of the elastomer structure is accomplished by changing theshear and compression/tension moduli by varying the strength of theapplied magnetic field. The MR elastomers typically develop theirstructure when exposed to a magnetic field in as little as a fewmilliseconds. Discontinuing the exposure of the MR elastomers to themagnetic field reverses the process and the elastomer returns to itslower modulus state. Suitable MR elastomer materials include, but arenot intended to be limited to, an elastic polymer matrix comprising asuspension of ferromagnetic or paramagnetic particles, wherein theparticles are described above. Suitable polymer matrices include, butare not limited to, poly-alpha-olefins, natural rubber, silicone,polybutadiene, polyethylene, polyisoprene, and the like.

MSMAs

MSMAs are alloys, often composed of Ni—Mn—Ga, that change shape due tostrain induced by a magnetic field. MSMAs have internal variants withdifferent magnetic and crystallographic orientations. In a magneticfield, the proportions of these variants change, resulting in an overallshape change of the material. An MSMA actuator generally requires thatthe MSMA material be placed between coils of an electromagnet. Electriccurrent running through the coil induces a magnetic field through theMSMA material, causing a change in shape.

Exemplary Embodiments of Telescoping Active Material Actuator Assemblies

Referring to FIG. 1, a first embodiment of an active material actuatorassembly 10 is illustrated. The active material actuator assembly 10 hasmultiple movable members 12, 14 and 16 and a fixed anchor member 18.Movable member 14 is referred to in the claims as the first movablemember and movable member 16 is referred to as the second movablemember. The movable members 12, 14 and 16 are preferably concentricbodies, which in cross-section may be circular, rectangular, triangularor any other shape, and are arranged in a “telescoping manner” such thatmovable member 12 is able to move at least partially in and out ofmovable member 14, which can move at least partially in and out ofmovable member 16, which can move at least partially in and out ofanchor member 18. In alternative embodiments, the movable members 12, 14and 16 need not be concentric. The telescoping movable members may bealigned to provide linear movement or may have a curved form to causenonlinear movement, such as along a circumference of a circle. Multipleactive material components are utilized to affect the telescopingmovement. An active material component 32 is connected at one end toanchor member 18 and at an opposing end to movable member 16. Activematerial component 32 is referred to as the first active materialcomponent in the claims. The active material component 32 is shownrouted through an opening in a proximal face 34 of movable member 16 andconnected to a distal face 36 of the movable member 16, but couldalternatively be connected to the proximal face 34. Active materialcomponent 38 is connected at one end to movable member 16 and at anopposing end to movable member 14. Active material component 38 isreferred to as the second active material component in the claims. Theactive material component 38 is shown routed through an opening in aproximal face 40 of movable member 14 and connected to a distal face 42of the movable member 14, but could alternatively be connected to theproximal face 40. Active material component 44 is connected at one endto movable member 14 and at an opposing end to movable member 12. Theactive material component 44 is shown routed through an opening in aproximal face 46 of movable member 12 and connected to a distal face 48of the movable member 12 but may alternatively be connected to theproximal face 46. End anchors 52 secure the respective ends of theactive material components 32, 38 and 44 to the respective movablemembers and the anchor member. The anchors 52 may be crimped portions ofthe respective active material components or may be any material capableof restraining an end of the active material component to the respectivemember, such as a rubber plug, a welded joint or adhesive/epoxy bondedjoint.

In FIG. 1, three active material components 32, 38 and 44 are shown.Within the scope of the invention, additional movable members connectedwith additional active material components may be used. Although theactive material components 32, 38 and 44 are depicted as elongatedwires, they may be rods, blocks, springs or any other shape capable ofcontracting upon activation (or deactivation). Finally, an activematerial component may consist of multiple discrete active materialelements such that multiple active material elements may be connectedbetween a pair of adjacent movable members or between the anchor member18 and movable member 16; i.e., sets of active material components maybe used. For example, an additional active material component 19 (shownin phantom) may be connected between the anchor member 18 and themovable member 16 in addition to the single active material component32. The active material elements may be in the form of wires or anyother geometric shape.

It should be appreciated that, within the scope of the invention, asingle active material component such as an SMA wire may be configuredwith different regions or segments connecting a movable member to afixed member having different active material properties such thatmodulated movement of a load attached to the movable member is achievedbetween the movable member and the fixed member via the differentregions of the single active material component actuating at differenttimes.

In FIG. 1, the movable members 12, 14 and 16 are shown at extremeextended positions, each not able to move any further out of therespective adjacent member due to flange-like stops 20, 22, 24 thatextend from the respective movable members 12, 14 and 16, to interferewith an inner surface of the respective adjacent members at openings 26,28, 30 in movable members 14, 16 and anchor member 18 through which themovable members 12, 14 and 16 translate, respectively. The stops 20, 22and 24 are integrally arranged such that movement of movable member 16to the right via contraction of active material component 32 pulls alongmovable members 12 and 14, and movement of movable member 14 to theright via contraction of active material component 38 pulls alongmovable member 12.

The active material components 32, 38 and 44 are shown in the stretched,extended state prior to activation. In the embodiment of FIG. 1, theactive material components 32, 38 and 44 are SMAs actuated at differentrespective temperatures which may be achieved by the temperature of thesurrounding fluid or by resistive heating serving as an activationsignal or trigger. The active material component 32 has the lowestAustenite start temperature, (As) followed by active material component38 and then active material component 44 (i.e., the active materialcomponents are arranged in ascending order of Austenite starttemperature (As) from the right). The transformation temperature rangesfor each of the active material components 32, 38 and 44 may becompletely distinct or may overlap. The temperature of the activematerial components 32, 38 and 44 could be increased by radiativeheating, resistive heating (see FIG. 5), fluidic (convective) heating(shown as an option in FIG. 1) or any combination of the above.

Return Mechanism

FIG. 1 contains three respective biasing springs 54, 56 and 58 acting asreturn mechanisms urging movable members 16, 14 and 12, respectively, tothe left (against return to original shape). The biasing springs 54, 56and 58 are optional because certain SMA materials with the reversibleshape memory effect have the ability to return completely to theiroriginal shape without the application of an external restoring force.Also, a restoring force (bias) could be introduced into a load attachedto the movable member 12 (or included in movable member 12).Furthermore, within the scope of the invention, a design with only onebiasing spring 54 could be used. Any other arrangement that puts biasingsprings in opposition to the recovery force (i.e., the contractionforce) of the active material components could be used, such asarranging the biasing spring external to the movable members 32, 38 and44 or using one biasing spring with the load for all of the activematerial components. Additionally, the stops 20, 22 and 24 act asoverstretch prevention mechanisms as they prevent stretching of theactive material components, (due to the return force of the springs 54,56 and 58, respectively) beyond the length determined by interference ofthe stops 20, 22 and 24 with respective movable members 14, 16 andanchor member 18.

For purposes of illustration, in the embodiment of FIG. 1, it is assumedthat activation is passively triggered by radiant heating and that theactive material components 32, 38 and 44 are exposed to the samesurrounding temperature. As the temperature of the active materialcomponents 32, 38 and 44 increases, the transformation of activematerial component 32 occurs first. Consequently, movable member 16 ispulled to the right and with it, due to the stops 20 and 22, movablemembers 12 and 14, and therefore the load, all working against the forceof biasing spring 54 (if used).

Modulated Movement

The total displacement achieved and force acting on the load attached tomovable member 12, due to the recovery force of the active materialcomponent 32, is illustrated by x₁ and F₁ in FIGS. 2 and 3 respectively.The displacement x₁ is indicated in FIG. 1 as movement of movable member12 from a start position 60 to an intermediate position 62. At thecompletion of the transformation of active material component 32 (orwhile transformation of active material component 32 is in progress ifthe transition temperature ranges of active material components 38 and32 overlap. This is illustrated by the dashed line in FIGS. 2 and 3 withthe overlap region between active material component 32 and activematerial component 38 represented by the interval t_(ov1). Activematerial component 38 begins to transform pulling with it movablemembers 12 and 14, and therefore the load. This causes an additionaldisplacement of the load of x₂ and the force acting on the load isincreased by Δ₂, illustrated in FIGS. 2 and 3. The displacement causedby activation of active material component 38 is indicated in FIG. 1 bymovement of movable member 12 from intermediate position 62 tointermediate position 64. Similarly as with the transformation of activematerial component 32, at the completion of the transformation of activematerial component 38 (or while the transformation of active materialcomponent 38 is in progress if the transition temperature ranges overlapas illustrated in FIGS. 2 and 3 with the overlap region between activematerial component 38 and active material component 44 represented bythe interval t_(ov2)), active material component 44 begins to transform,thereby pulling with it movable member 12 and working against theopposing force of spring 58. At the completion of the transformation ofactive material component 44, there is an additional displacement of theload of x₃ and the force on the load is increased by Δ₃, illustrated inFIGS. 2 and 3. The displacement caused by activation of active materialcomponent 44 is indicated in FIG. 1 by movement of movable member 12from intermediate position 64 to intermediate position 66 in FIG. 1.

In FIGS. 2 and 3, the increments in load displacement (x₁, x₂ and x₃)and in force (F1, Δ₂ and Δ₃) appear equal for purposes of illustrationonly, but could be different depending on the characteristics of theactive material components 32, 38 and 44 and the biasing springs 54, 56and 58 and the kind of load that is attached to the movable member 12.For example, it may be desirable to select the active materialcomponents such that some actuate quickly and achieve a relatively largedisplacement, followed by later actuation of another active materialcomponent to achieve a relatively small displacement. For example,active material components 32 and 38 may actuate at lower temperaturesand may be selected to contract a relatively large amount, followed byactuation of active material component 44 which may actuate at arelatively high temperature and contracts a lesser amount. The actuationof the earlier actuated active material components may also occur morequickly than the actuation of the later actuated active materialcomponent to achieve a fast initial displacement followed by a slowermovement to the final load position. In this way, the earlier actuatedactive material components accomplish coarse tuning or positioning ofthe load, while the later actuation fine-tunes the load position. Suchan arrangement may simplify a control system designed to control thefixed position of the load. If all but one of the active materialcomponents actuate simultaneously to accomplish the coarse turning andthe fixed active material component accomplishes fine tuning, thecontrol system need only monitor the position of the load after thecoarse tuning (i.e., monitor a single measurement of the initial,relatively large coarse-tuned displacement) to provide feedback foraccurate positioning during fine tuning, rather than monitoring a seriesof displacements by actuation of active material components at differenttimes that achieve the coarse tuning. This avoids the cumulative errorassociated with a series of discrete control measurements and alsosimplifies any overall control design. It is to be further appreciatedthat a load that linearly increases with displacement is assumed in theillustrations of FIGS. 2 and 3.

The distinct or overlapping transformations of the different activematerial components 32, 38 and 44 give rise to a modulated displacementprofile of the load connected to movable member 12. The result is that alarger displacement is obtained than with a single active materialcomponent or than with multiple active material components spanning fromthe distal face 48 of movable member 12 to the portion of anchor member18 at which active material component 32 is connected. Furthermore, therecovery force is modulated as shown in the illustration of FIG. 3. Thestress on the active material components 32, 38 and 44 continuallyvaries with the actuation of each subsequent active material component(assuming no optional locking/latching mechanisms, as in the descriptionbelow). It is preferable to ensure that the maximum stress in eachactive material component does not exceed the value required foracceptable performance. If the surrounding temperature decreases, theactive material components 32, 38 and 44 will be restored to theirmartensite phase lengths (i.e., the movable members will return to thepositions shown in FIG. 1) due to the load and the biasing force of therespective springs 54, 56 and 58 (if used), in order as temperaturedecreases.

Preferably the recovery force of active material component 44 is largerthan that of active material component 38 which in turn is larger thanthat of active material component 32. This is especially useful iflocking mechanisms are used after the actuation of each active materialcomponent thereby isolating the active material component and allowingthe next active material component to have a larger recovery force.

In FIGS. 2 and 3, curves 70 and 72, shown with solid lines, representthe load displacement profile and the load holding force profile,respectively, for the case where transformation of each active materialcomponent is completed before the subsequent one begins. Transformationof active material component 32 begins at time t=0, and is completed attime t=t₁. There is a hold period until time t=t_(h1) when thetemperature of the active material component 38 reaches its austenitestart temperature, at which point transformation of active materialcomponent 38 begins and continues until time t=t_(h1)+t₂. Again, thereis then a hold period until time t=t_(h2) when active material component44 reaches its austenite start temperature, at which pointtransformation of active material component 44 begins and is completedat time t=t_(h2)+t_(h3). The flat sections of curves 70 and 72 describethe hold periods where no transformation is taking place.

For an embodiment where the compositions of the active materialcomponents 32, 38 and 44 are such that the transformations overlap, thetypical load displacement profile and load holding force profile areillustrated by curves 74 and 76, respectively. For instance, in FIG. 2,the overlap in the transformation of active material component 32 andactive material component 38 occurs over time t_(ov1). During this time,the rate of transformation of active material component 32 increases asactive material component 38 begins to transform. At full transformationof active material component 32 the rate of transformation of activematerial component 38 continues as described earlier. A similar effectoccurs over time t_(ov2) for the overlap of active material component 38and active material component 44. The description above is forillustrative purposes only and the response profile of each activematerial component, distinctly or during overlap, would generally dependon the composition of the active material component and the heattransfer process between the activation input trigger, whether anactuating field, fluid or current, and the active material component.For instance, the transformation rates shown as constant would generallybe nonlinear.

Referring again to FIG. 1, if active convective (fluid) heating wereused instead of passive radiant heating, openings 80, 81, 82 and 83would be provided in the respective anchor member 18, and in movablemembers 14, 16 and 12. Arrows A illustrate the direction of fluid flowthrough the openings 80, 81, 82 and 83 for the general case where thesame fluid flows past the different active material components 32, 38and 44 at the same time. Alternatively, if resistive electrical heatingis used, the right end of each active material component could beconnected to an electric lead, e.g., a positive electric lead, and theleft end would be connected to the opposite electric lead, e.g., anegative electric lead, (i.e., at the anchors 52) with suitableinsulation. Current could be supplied to the different active materialcomponents 32, 38 and 44 in series or parallel, at the same time or in adefined sequence, depending on the desired force/displacement profile.

Referring to FIG. 4, another embodiment of an active material actuatorassembly 110 is illustrated. The active material actuator assembly 110includes movable members 112, 114, and 116, anchor member 118 and activematerial component 132, 138 and 144 operable in like manner as similarlynumbered components in FIG. 1. A load 119 is connected to movable member112 such that it is moved therewith. Each of the movable members 112,114 and 116 form a frame around an intermediate resilient portion whichin this embodiment is bellows 113, 115 and 117, respectively. Thebellows 113, 115 and 117 are made of a suitable material, such ashydroformed metal, and are attached by any suitable means to the movablemembers 112, 114 and 116, respectively. The bellows are a flexiblematerial that compresses in width as the active material components 132,138 and 144 contract and the movable members 112, 114 and 116 move tothe right. Biasing springs 154, 156 and 158 may be placed in compressionwithin respective movable members 116, 114 and 112 to oppose therestoring force of the active material components 132, 138 and 144. Thebiasing springs could alternatively be placed in a similar position assprings 54, 56 and 58 in FIG. 1. As an alternative to the biasingsprings 154, 156 and 158, the required bias could be built into all ofthe bellows 113, 115 and 117 or only into bellows 117 to function as areturn mechanism resisting the first-activated active material component132. Alternatively, the active material components used could havereversible shape memory effect in lieu of the biasing springs orbellows.

Automatic Activation

Automatic activation mechanisms could be integrated with the inventionso that, assuming active activation, the activation input (i.e.,actuating field, fluid or current), is transferred to a succeedingactive material component when the preceding active material componentreaches a predetermined level of change in a property such as apredetermined level of strain (e.g., a percentage of the maximumpossible strain, for safety and/or durability), or when transformationis complete in order to maximize the output of the actuator assembly.That is, movement of a first moveable member via an activation input toa first active material component causes an activation input to a secondactive actuation mechanism to activate a second active materialcomponent. As illustrated in FIG. 5, an active material actuatorassembly 210 with movable members 212, 214, 216 and anchor member 218includes an extension 290 on movable member 216 configured to contactextension 291 on anchor member 218. (Movable member 212 is shownfragmented, but connects to a load similarly to movable member 112 ofFIG. 4.) At the completion (or at a predetermined level) of thetransformation of active material component 232, the extension 290 fitsinto and contacts extension 291. This action allows the electric circuit(between positive electric lead 292 and negative electric leads 293) foractive material component 238 to be completed, thereby allowing currentto flow through the active material component 238 to cause itstransformation to the austenite phase. Various ways could be used toensure that the electric supply is well insulated from the rest of theactive material actuator assembly 210, for instance, by using amale/female connection system on the extensions 290 and 291. In otheralternative embodiments, the contact between the extension 290 andextension 291 need not directly complete the actuating electric circuitbut can be used to trigger the sending of a signal to a control system(not shown) to supply current for the activation of active materialcomponent 238 in the case where this is desired. Similar extensionscould be added between movable members 214 and 216, to cause automaticactivation of active material component 244. In the case of activeactivation via convective heating, the contacting extensions could eachhave a hollowed conduit to allow the transfer of heating fluid throughthe conduits to heat a subsequent active material component when theextensions contact one another. For example, one end of one extensioncould cause a valve or orifice on the second extension to open, therebyallowing fluid flow which can be routed over the active materialcomponent.

Locking Mechanism and Releasing Mechanism

A locking mechanism or mechanisms could be integrated in an activematerial actuator assembly to lock adjacent movable members to oneanother to thereby achieve holding of the movable members in an actuatedposition during a power-off condition. In FIG. 6, an active materialactuator assembly 310 (shown only in part, but similar to any of theactive material actuator assemblies of FIGS. 1, 4 or 5), optionallocking mechanism 394 connects movable member 316 to anchor member 318at the completion of the transformation or at the required level oftransformation (i.e., actuation) of an active material component (notshown) connected between movable member 316 and anchor member 318, wherethese features operate as like numbered components in the activeactuator assembly 210, i.e., of FIGS. 1, 4 or 5. Similar mechanismscould be used between other pairs of adjacent movable members in theactuator assembly 310. More flexibility is obtained in the level of loadholding force obtained at each phase (i.e., at the time periodassociated with contraction of each active material component) since thetotal force at each stage could be more than the specified limitingforce of the active material component in the preceding stage, as thepreviously activated active material component is isolated by thelocking mechanism. For example, the load holding force could be greaterthan the specified limiting force of the active material component thatconnects movable member 316 to anchor member 318 after locking of thelocking mechanism 394 as the load is then borne by the locking mechanism394. Any suitable locking mechanism could be used, including thosedescribed with respect to other active actuator assembly embodimentsherein. For instance, in the assembly 310 shown in FIG. 6, the arm 395is attached to the movable member 316 and the extension 396 is attachedto the anchor member 318. As the transformation to the fully austenitephase of an active material component connected between movable member316 and anchor member 318 progresses, movable member 316 is free totranslate. Locking occurs when the arm 396 fits into the notch 397 inarm 395 as shown. During the movement to the left of movable member 316(in the forward transformation to the martensite phase), the lockingmechanism 394 is releasable via an upward force (indicated by arrow C)applied to downward extension 389 on extension 396, compressing spring399 and thereby pivoting arm 396 about pivot point B to allow itsrelease from the notch 397.

Exemplary Embodiment of An Alternative Active Material Actuator Assembly

Referring to FIG. 7, another active material actuator assembly 410utilizes a “train carts on a railroad” approach to achieve large lineardisplacement. The active material actuator assembly 410 includes movablemembers 412, 414 and 416, a fixed member 417 and an anchor member 418,all of which are linearly aligned on a base member 421. The movablemembers 412, 414 and 416 slide or roll with respect to the base member421, similar to train cars on a railroad track. Although only threemovable members are included in the actuator assembly 410 of FIGS. 7-9,it should be understood that only two movable members or more than threemay alternatively be used. The fixed member 417 and the anchor member418 are secured to and do not move with respect to the base member 421.The interface between the movable members 412, 414, 416 and the basemember 421 could be any shape and configuration. In cross section, thebase member 421 could be circular, oval, rectangular, triangular,square, etc., as long as the movable members 412, 414 and 416 areconfigured with a mating shape to partially surround the base member.The interface can also be in a dove-tailed shape as shown in FIG. 7. Asan alternative approach, the base member 421 could have multiple slots,one for each movable member. It is therefore very easy to preventoverstretching and release each movable member at the appropriatelocation, as the distal end of a slot will always be the desiredlocation for release of a movable member.

With regard to FIG. 7, the movable members 412, 414 and 416 areconnected to the anchor member 418 via respective active materialcomponents 444, 438 and 432, respectively. The movable members 414 and416 and the fixed member 417 have a set of aligned openings therethroughthat allow active material component 444 to pass through to connect at adistal end to the movable member 412 and at a proximal end to the anchormember 418, as illustrated. Movable member 416 and fixed member 417 haveanother set of aligned openings that allow active material component 438to pass through to connect at a distal end to movable member 414 and ata proximal end to anchor member 418. Finally, fixed member 417 has yetanother opening therethrough that allows active material component 432to pass through to connect at a distal end to movable member 416 and ata proximal end to anchor member 418. The ends of each active materialcomponent 432, 438 and 444 are crimped (or attached by any othersuitable means such as welding or adhesive bonding) to maintainpositioning. In an alternative design, the active material components432, 438 and 444 connect a respective extension (e.g., a rod or bar)extending from the respective movable member to an extension (e.g. a rodor bar) extending from the anchor member 418 rather than passing throughopenings in the movable members and the fixed member. To avoid bendingand to increase fatigue life, the crimped ends of the active materialcomponents 432, 438, and 444 at the anchor member 418 are able to sliderightward during actuation. It is preferred that the bending momentum onthe actuator assembly 410 induced by the active material components 432,438 and 444 is minimized by design choice of active materialcomposition, cross-sectional area of the active material components andthe structural strength of the base member 421, the movable members 412,414, 416, fixed member 417 and anchor member 418. The active materialcomponents 432, 438 and 444 are shown in extreme extended positions, ina martensite phase, in which the movable members 412, 414 and 416 willnot move further to the left. The movable members 412, 414 and 416 caneither roll (via wheel(s) attached to respective movable member with orwithout bearings), slide or slide and roll on the base member 421 andare separated from each other by predetermined distances according todesign. Optionally, multiple anchor members may be utilized so that theproximal ends of the active material components 432, 438 and 444 can beat different longitudinal locations with respect to the base member 421.A load or force that is to be moved by the active material actuatorassembly 410 is either formed by the movable member 412 or ismechanically linked to a distal side of it. The load or force may be aweight or spring configured to act as a return mechanism (i.e., tocreate a force biased against contraction of the active materialcomponents 412, 414 and 416).

When active material component 444 is activated (by supplying electricalcurrent, as will be discussed below), the recovery or contraction forceof the active material component 444 is greater than the totalresistance of the load, and the movable member 412 is pulled to theright toward movable member 414. When movable member 412 moves close tomovable member 414, they lock together via a locking mechanism such asthat described in detail with respect to FIG. 8. Next active materialcomponent 438 is activated to bring movable members 412 and 414 (lockedtogether) to movable member 416. When movable member 414 is close tomovable member 416, they lock together by locking mechanism such as thatdescribed with respect to FIG. 8. Similarly, when active materialcomponent 432 is then activated, locked-together movable members 412,414 and 416 move to the right and movable member 416 is locked to thefixed member 417 by a locking mechanism as described with respect toFIG. 8.

Locking Mechanism, Releasing Mechanism and Overstretch PreventionMechanism

With reference to FIGS. 7 and 8, each movable member 412, 414, 416includes a locking mechanism. Locking mechanism for movable member 412includes latch 495A, pin 497A and spring 499A. Latch 495A is able toenter a slot formed in movable member 414 and go further with pin 497Apassing through due to a slotted keyhole 496A (see FIG. 7) in the frontwith a width slightly wider than the diameter of a pin 497A retained inan opening within the movable member 414. When movable member 412touches movable member 414, the keyhole 496A in latch 495A is exactlyunder the pinhead (i.e., a double-flanged head) of pin 497A. With alittle more shrinking of the active material component 444 (see FIG. 7),the latching pin 497A will move downward due to the slope of ramped key498A and the biasing force of spring 499A, to fall within the keyhole inlatch 495A. The uppermost flange on the pin 497A is larger than thebottom hole of movable member 414 and thus rests above it to ensure thatthe pin 497A rests in the latch 495A to latch movable members 412 and414 together. Movable member 414 (with movable member 412 latched to it)is locked to movable member 416 in like fashion as active materialcomponent 438 contracts, and movable member 416 (with movable members412 and 414 locked to it) is locked to fixed member 417 in like fashion.

The releasing of the latches is in exactly the reverse order and will bedescribed with respect to the release of movable member 412 from movablemember 414. When movable members 412 and 414 are pulled leftward inFIGS. 7 and 8 together by the load after actuation when conditions allowactive material component 444 to return to its martensite phase,latching pin 497A touches the slope in the key 498A, rides up the slope,and the pin 497A is moved upward until it slides into an upwardlyextending stopper portion of the ramped key 498A. The stopper portionacts as an overstretch prevention mechanism, preventing further movementto the left. At this point, the bottom of the lower flange of thedouble-flanged head of the pin 497A (see FIG. 9 for a view of thedouble-flanged head) is flush with the top of the latch 495A andtherefore releases it. Similar latches, latching pins and ramped keysare utilized between movable members 414 and 416 and between movablemember 416 and fixed member 417.

The release of a movable member by releasing the latch must be done whenthe movable member is at the pre-contraction (original stressed)position. Otherwise, the active material component attached to themovable member may not be stretched enough for next activation and amore distal movable member (activated just prior) will not be able tolock to it. Therefore, the keys 498A-498C are positioned in base member421 at the desired start position of the movable members 412, 414 and416 or the position of fixed member 417.

Since the latching pins 497A and 497B move together with the respectivemovable members 414 and 416, they should not be blocked by keys 498B and498C, respectively, when moving in the proximal direction. For example,in the fully locked position, the bottom of pin 497A should be slightlyhigher than that the top of key 498B. FIG. 9 illustrates that the shankportion of the pins 497A, 497B, and 497C have respectively longerlengths and the keys 498A, 498B and 498C are in order of descendingheight (key 498A not shown in FIG. 9) so that the more distal movablemember, will pass over the more proximal keys during return to thepre-contraction position. The sum length of each locking pin 497A-497Cand its matching ramped key 498A-498C is the same for movable members414 and 416 and fixed member 417. Alternatively, to reduce the overallheight in comparison with actuator assembly 410, movable members withdifferent widths can be used with keys offset along a horizontaltransverse direction such that the keys can be of same height.

Although only one locking mechanism is shown here, any other existingmechanisms or new mechanisms can be adapted for use with any of theactive material actuator assemblies described herein, such as asolenoid-based locking mechanism, a smart materials-based lockingmechanism, a safety belt buckle-type latch design, or a toggle on-offdesign such as in a child-proof lock/release for doors or drawers or ina ball point pen. For example, the cart may have a keyhole, such as aT-shaped slot on a surface facing an adjacent cart. The adjacent cartmay have a latch designed to fit in the upper portion of the T-shapedslot (i.e., the horizontal portion of the T-shape) and slide into thelower portion (i.e., the vertical portion of the T-shape) when the cartwith the latch moves along a ramped track toward the cart with theT-shaped slot to lock the two carts to one another. The slope of theramped track is designed to cause the relative vertical displacementbetween the two carts that enables latching and releasing of the latchfrom the T-shaped slot.

Other examples of locking and release mechanisms include a lockingmechanism having a latch on one movable member that is configured toslide into a slot of an adjacent movable member. A separate releasemember can be actuated to push the latch out of the slot, thus releasingthe two movable members from one another. The release member may be aroller attached to the end of a spring. The latch rolls along the rollerwhen released, thus avoiding direct contact with the adjacent movablemember during its release and reducing friction associated with therelease movement.

Holding Mechanism

Power off holding is desirable for either full displacement (when themost proximal movable member 416 is locked to the fixed movable member417) or at discrete displacement when a movable member is locked to thenext movable member. Power off holding means utilizing a holdingmechanism to hold a movable member at a post-activation contractedposition, when the activation input is ceased (e.g., when the power isoff if resistive heating is used or if temperature cools below theAustenite start temperature in the case of convective or radiantheating). For the embodiment shown in FIG. 8, the key 497A can belowered down to lock movable members 412 and 414 together. By moving asliding block 484 underneath the base member 421 along the longitudinaldirection, the keys 498A-498C will move off of raised bumps 485 on block484 and be lowered down due to spring force exerted by springs499A-499C. With the keys 498A-498C in a lowered position, even thoughthe locking pin 497A of movable member 414 slides on the slope of key497A during return of the active material component 438 to themartensite phase, key 497A will not be able to push the locking pin 497Afar enough up in order for the lower surface of the lower flange of thepinhead to clear the keyhole opening in latch 495A. Moving the slidingblock 484 will cause holding of the movable members at the keyassociated with the most proximal of the movable members which have beenmoved or at the fixed member 417 if all of the movable members havealready been moved to the right when the sliding block 484 is moved. Tocancel the holding in order to release the movable members, the slidingblock 484 can be moved back so that all the keys 497A-C are pushed up.The vertical displacement of the keys via the sliding block 484 is smalland the horizontal movement of the sliding block 484 can be achieved viamany mechanisms, such as an electronic solenoid or a short SMA wire.

An alternative holding mechanism is illustrated in FIG. 7 with respectto movable member 412. The alternative holding mechanism includes a pawl486 and a ratchet portion 487 of the base member 421. The pawl 486allows the movable member 412 to be held at any position. To release themovable member 412, the pawl 486 is pulled away (either rotated upwardor pulled upward) from the ratchet portion 487 by a mechanism (notshown) such as an electronic solenoid or a short SMA wire.

Automatic Activation

The active material actuator assembly 410 can automatically mechanicallyactivate the active material components sequentially to eliminatecontrol logic and therefore reduce the cost. To realize this, theproximal ends of the active material components 432, 438 and 444 at theanchor member 418 are all connected to the negative pole of the electriccurrent supply, such as a battery (supply not shown) and the positivepole of the electric current supply is connected to separate electricalcontact strips 491A, 491B and 491C each located on the base member 421between movable members (see FIG. 7). The bottom of each movable member412, 414 and 416 has its own specific electrical contact strip runningfore and aft (in the same direction that the movable members 412, 414and 416 move) that is aligned with a specific electrical contact stripon the base member 421. For example, referring to FIG. 7, movable member412 has electrical contact strip 490A (shown with dashed lines) on abottom surface thereof that is aligned with electrical contact strip491A (also referred to herein as a first active material activationmechanism) on the base member 421. Movable member 414 has an electricalcontact strip 490B on a bottom surface thereof that is aligned withelectrical contact strip 491B (also referred to herein as a secondactive material activation mechanism) on the base member 421. Movablemember 416 has an electrical contact strip 490C (shown with dashedlines) on a bottom surface thereof that is aligned with electricalcontact strip 491C on the base member 421. The active material componentconnected to each distal movable member always maintains electricalcontact with the electrical contact strip on the bottom of the movablemember it is attached to. When a switch (not shown) is turned on toallow power flow from the electric current supply, active materialcomponent 444 will be in a closed circuit (the circuit including theelectrical contact strip 490A, the electrical contact strip 491A, theactive material component 444 and the power leads) causing activematerial component 444 to contract and move movable member 412 towardmovable member 414. After movable members 412 and 414 lock together,further movement of movable member 412 will cause electrical contactstrip 490A to be out of contact with electrical contact strip 491A onthe base member 421 and will cause the electrical contact strip 490B atthe bottom of movable member 414 to be in contact with electricalcontact strip 491B on the base member 421. At this point, activematerial component 444 is in open circuit and active material component438 is in closed circuit. Thus, an activation input to the secondmovable member, i.e., power from the electric current supply attached tothe power leads, activates the active material component 438 to move themovable member 414 (and movable member 412 locked thereto). This“automatic activation” of the next active material component viamovement of the previous movable member will be repeated until themovable member 416 reaches fixed member 417. By using a contact switchon movable member 417, the power can be turned off.

By locking each locking mechanism as each respective active materialcomponent 444, 438, and 432 contracts, the load operatively attached tothe first movable member or the first movable member itself has a traveldistance equaling the sum of the respective gaps (i.e., the open spacealong base member 421) between movable members 412 and 414, betweenmovable members 414 to 416 and between movable member 416 and fixedmember 417. To return the load back toward the distal end of base member421, the holding mechanism is first released (i.e., sliding member 484is moved) if it was utilized, and the latch 495C is released from thelocking pin 497C. As the active material component 432 is cooled andapplies less resistance to stretching, the force of the returningmechanism also referred to as the load (e.g., a dead weight, a constantspring, a linear spring, a strut) is able to pull all the movablemembers 412, 414 and 416 toward the distal end of the base member 421.When movable member 416 is closer to its designed pre-contractionposition, the latching between latch 495B and locking pin 497B isreleased by ramped key 498B and therefore movable member 416 can bedetached from movable members 412 and 414. Similarly, movable member 414will detach from movable member 412 and stop at the designedpre-contraction location due to the ramped key 498A.

Large displacement can be achieved by the active material actuatorassembly 410, as many movable members can be added. The surface areabetween the movable members and the base member 421 (on which themovable members slide, roll or roll and slide) can be minimized toreduce friction losses. Finally, the returning force of the load can bematched very easily by a load holding force profile as the size ornumber of active material components, the composition and/or thetransformation temperatures can be different for different movablemembers. Therefore, any returning mechanism such as strut, dead weight,linear spring, constant spring etc. can be chosen for convenience andperformance. To have proper fatigue life and for safety and reliability,it is important that the active material components are notover-stretched by the returning mechanism.

In the embodiment shown in FIG. 8, all of the movable members 412, 414and 416, and the fixed member 417 have same sized components (the bodyof movable member or fixed member, the latches 495A-495C, the setscrewat the top of each movable member 412, 414, 416 and fixed member 417 toadjust the tension of springs 499A-499C) as shown in movable members412, 414 and 416, as well as components of varying dimension (lockingpin 497A and ramped key 498A) as shown in and discussed with respect toFIG. 9.

FIG. 9 shows movable member 412 locked to movable member 414 which islocked to movable member 416. Key 498B acts as a power off holdingmechanism as it is raised by bump 485 to interfere with pin 497B. FIG. 9illustrates the positioning just prior to automatic activation of activematerial component 432 (not shown in this cross-section) to movemoveable member 416 to lock to fixed member 417.

Exemplary Embodiments of Other Active Material Actuator Assemblies

Referring to FIG. 10, an active material actuator assembly 510 includesa movable member in the form of a shaft 512 that is rotatable about acenter axis 513. The shaft 512 is concentric with an opening of a basemember 517 and rotates therein. Optionally, a bearing may be placedbetween the shaft 512 and the base 517 to aid rotation. Referring toFIG. 11, on an opposite side of the base 517, a cam lobe 519 isconnected for rotation with the shaft 512. Referring again to FIG. 10,an extension member, which may be referred to herein as a pin 521extends from the shaft 512 such that it is offset from and parallel withthe center axis 513. Multiple active material components 532, 538, 539and 544, shown in the form of wires (but which may be belts, straps,strips, thin plates, chains or other shapes), have one end attached tothe pin 521. Active material component 532 is bent over pulley 523A andfurther bent over pulley 525A and extended toward the bottom of the base517 where an end is attached to retaining pin 527A. Active materialcomponent 538 is bent over pulley 523B and extends toward the bottom ofthe base 517 where it attaches at an end to retaining pin 527B. Activematerial component 539 is bent over pulley 523C and extends toward thebottom of base 517 where it attaches to retaining pin 527C. Activematerial component 544 is bent over pulley 523D and further bent overpulley 525B and extends toward the bottom of base 517 where it attachesto retaining pin 527D. As an alternative to the pulleys 523A-D and525A-B, gears may be used with the active material components 532, 538,539 and 544 (or at least a nonactive wire portion connected thereto)being in the form of chains. The pulleys 523A-523D (or gears if usedinstead of pulleys) are also referred to herein as sliding elements.

By bending the active material components 532, 538, 539 and 544 viapulleys 523A-D and 525A-B to extend in a common direction, packagingsize is greatly reduced, with only one long dimension (the distancebetween the pulleys and the retaining pins at the bottom of the basemember 517) accommodating the length of the active material components.Optionally, to avoid fatigue degradation due, directly or indirectly, tobending of the active material components, regular metal wires (orbelts, strips, etc.) having long fatigue life may be used for anyportion experiencing bending and active material composition may be usedonly for the portion from the respective pulleys 525A, 523B, 523C and525B to the retaining pins 527A-D (i.e., the portion that remainsstraight throughout the actuation cycle).

The base member 517 has multiple slots 529A, 529B, 529C and 529Dextending therethrough. Extension portions of the pulleys 523A, 523B,523C and 523D extend through the respective slots 529A, 529B, 529C and529D so that a portion of each pulley is in contact with a cam surface531 of the cam lobe 519.

Resetting Cooled Active Material Components and Avoiding Stretching ofHot Active Material Components

The active material components 532, 538, 539 and 544 can be actuated inthat order in a repeating series (or in the reverse order in a repeatingseries) to move the pin 521 and therefore rotate the shaft 512 to whicha load is attached (or which constitutes a load). Both clockwise andcounterclockwise rotation can be equally achieved in the actuator 510 byreversing the order of actuation. To avoid overstretching, to decreaseresistance to stretching of a just actuated and still hot activematerial component and to decrease response time, the pulleys 523A-523Dare designed to move in the respective slots 529A-529D according to thecam surface 531 (i.e., the cam profile) of the cam lobe 519, shown inFIG. 11. In FIG. 11, pulleys 523C and 523D are shown on a larger arc ofthe cam surface 531 and in the farthest position relative to the centeraxis 513. In contrast, pulleys 523A and 523B are on a smaller arc and inthe nearest position relative to the center axis 513. The pin 521 isnearest to pulley 523C (see FIG. 10), active material component 539(referred to in the claims as the first active material component) hasjust been actuated and it is time to activate active material component544 (referred to in the claims as the second active material component).During the contraction of active material component 544, pulley 523Dwill sit on the: larger arc and remain a constant distance to the centeraxis 513. The pin 521 will be pulled and moved toward pulley 523D.Pulley 523C will move toward the center axis 513 because it will be onthe smaller arc when pin 521 moves near pulley 523D. Due to this inwardmotion of pulley 523C sliding in slot 529C toward the center axis 513,the previously actuated and potentially not yet cooled active materialcomponent 539 will not be further stretched and will apply no resistanceto the work done (i.e., to the rotation of shaft 512) by actuation ofactive material component 544 provided the portion of active materialcomponent 544 (or wire if that portion is not active material) betweenpulley 523C and retaining pin 527C is barely stretched. This portion ofactive material component 544 between pulley 523C and retaining pin 527Cwill change in length only a minimal amount if it is nearlyperpendicular to the longitudinal direction of the slot and if it ismuch longer than the longitudinal dimension of the slot. FIG. 10 isschematic in nature and the dimensions are not to scale. Positions andshapes of the slots and positions of the retaining pins are alsoschematic. In addition, additional pulleys (not shown for simplicity)may slide with pulleys 523A-D and help with the routing of the activematerial components. Although pulley 523B sits on the same smaller arcduring this period, the cooled active material component 538 isstretched since pin 521 moves near to pulley 523D from a position nearpulley 523C. Pulley 523A increases its distance from the shaft centerduring this period since the rotating cam 519 causes it to slide in slot529A and move to a larger arc, maintaining the length of the activematerial component 532 between pin 521 and pulley 523A. When activationof active material component 544 is complete, active material component532 is in the right position and ready for a subsequent activation.

Within the scope of the invention, the number of active materialcomponents is not limited to four. A rotational motor as in FIGS. 10 and11 could haven only three or more than four active material components.Furthermore, the slots 529A-D are not limited to the shape shown. Acenter line running the length of each slot does not necessarily passthrough the shaft center and need not be straight.

Automatic Activation

Sequential automatic activation by the mechanical rotation of the shaft512 can be utilized to allow the elimination of control logic toactivate the active material components 532, 538, 539 and 544sequentially and therefore potentially reduce cost. The four individualends of the active material components connected to pins 527A through527D can be connected to the negative pole of a battery (not shown).Referring to FIG. 12, the positive pole of the battery is connected to aswitch 589 and then connected to an electrical brush 533 on the camsurface 531 of cam 519. An electrical contact strip 535 extendspartially around the cam surface 531. The contact strip 535 is inelectrical contact with a circular electrical strip 537 on the camsurface 531 that touches the brush 533 at all times. On the surface ofeach pulley 523A, 523B, 523C and 523D that touches the cam surface 531,there is a circular electrical contact strip 541A, 541B, 541C and 541D,respectively, positioned to be sequentially in contact with the contactstrip 535 as the shaft rotates. The circular electrical contact strip541A-541D on each pulley 523A-523D is electrically connected to thesurface area of the pulley that the respective active material componentis touching (or that a non-active material portion, e.g., a metalportion of a wire, strip, chain or belt that is connected to an activematerial portion, as explained above, is touching). All surface areas ofthe cam surface 531 and of the pulleys 523A-523D are non-conductingexcept those mentioned above.

When the switch 589 is closed (i.e., by turning on the actuator assembly510), electrical power runs to the full circle electrical contact strip537 and to whichever one of the pulleys 523A-523B is then positioned incontact with the contact strip 535 (pulley 523C in FIG. 12). The activematerial component connected with that pulley is activated to move thepin 521. Movement of the pin 521 due to actuation of that activematerial component, as described above, will rotate the cam 519, causingthe next sequential one of the pulleys to be positioned in contact withthe electrical contact strip 535 to activate the active materialcomponent connected thereto (and will cause the previously actuatedactive material component to move out of contact with the contact strip535). The contact strip 535 may extend 90 degrees or so around the camsurface such that only one of the four pulleys 523A-532D is in contactwith the contact strip 535 at any given time. Alternatively, the contactstrip may extend less than 90 degrees, to allow a longer cooling periodbetween activations, or greater than 90 degrees such that there is someoverlap of activation of the active material components. The portion ofthe cam profile 519 about which the contact strip 535 extends may belonger if only three active material components and correspondingpulleys are used, or shorter if more than four are used. In general, theportion over which the contact strip 535 extends is cam-profiledependent.

Power off holding of the active material actuator assembly 510 isdesirable. It can be realized via the locking mechanism (andcorresponding release mechanism) similar to that described with respectto the active material actuator assemblies 410 above or a ratchetmechanism.

Another embodiment of an active material actuator assembly 610 operatingas an incremental rotational motor is shown in FIG. 13. A shaft 612 withan extension or pin 621 is concentric with a hole through a cylindricalhousing 617 and rotates with or without the help of a bearing. Activematerial components 632, 638, 639 and 644 are attached to the biased pin621 at one end, bent over pulleys 623A-D and 625A-D and attached toretaining pins at the other end of the cylindrical housing (pins notshown, but FIG. 14 shows the active material components in fragmentaryview extending toward the pins). The pulleys 623A-D and 625A-D sit onsliders 643A-D that slide in slots 629A-D of the cylindrical housing617. The active material components 632, 638, 639 and 644 can beactivated sequentially and therefore rotate the shaft 612 with respectto the cylindrical housing 617. Since all the active material components632, 638, 639 and 644 are bent (via the pulleys 625A-D) to extend in theaxial direction of the shaft 612, sufficiently-sized active materialcomponents able to achieve large displacement (e.g., active materialcomponents of a sufficient length to achieve adequate displacement ofthe movable member via contraction of each active material component)are enabled while packaging size is minimized. Optionally, to avoidfatigue degradation due to bending of active material components,non-active material portions (e.g., regular metal wire) having longfatigue life can be substituted for any portion of the active materialcomponents experiencing bending and active material can be used only inthe portion that remains straight throughout the actuation cycle, i.e.,the portion nearly parallel to the axial direction of the shaft 612.

The sliders 643A-643D ride on a cam lobe 619 of the shaft 612. The camprofile 631 (shown in the FIG. 14) allows the slider to which thejust-actuated active material component is operatively connected to movetoward the center of the shaft 612 and therefore prevents being pulledby the next-actuated active material component. The cam profile 631therefore utilizes the contraction force of the active materialcomponents more efficiently (i.e., utilizes the force to turn the shaftrather than to work against restrictive force of the just-actuatedactive material component), allows more cooling time before stretchingof a previously actuated component, and decreases the cycle time of theactuator assembly 610. The cam profile 631 can also be made to avoidunnecessary overstretching of the active material components. In FIGS.13 and 14, each active material component is only stretched by theopposite actuated active material component (i.e., active materialcomponent 644 is stretched when active material component 638 isactuated and vice versa, and active material component 639 is stretchedwhen active material component 632 is activated and vice versa) and theamount of stretch is the same as the amount needed to pull the pin 621and rotate the shaft 612 when it is actuated.

Automatic activation is possible which will eliminate the use of controllogic to activate wires sequentially and therefore reduces the cost. Byproviding an electrical contact strip only partially extending aroundthe cam surface similarly to electrical contact strip 535 in theembodiment of FIG. 12, the respective active material components will beactivated sequentially as the shaft 612 rotates. Power off holding isdesirable and it can be realized via a ratcheting or locking andreleasing mechanisms, as described with respect to other embodimentsherein.

Note that in the active material actuator assembly 610, the number ofactive material components is not limited to four. There could be onlythree active material components or more than four. The slots 629A-D arenot limited to the configuration shown. The center line of the slotsdoes not necessarily pass through the shaft center and is notnecessarily straight. In addition, both clockwise and counterclockwiserotation can be equally achieved in the said mechanism. Moreover, toreduce response time and decrease cooling time while maintainingrequired force, several thinner SMA components can be used in place ofeach active material component (e.g., several thinner SMA wires in placeof each single SMA wire) to connect the distal end.

While the best modes for carrying out the invention have been describedin detail, those familiar with the art to which this invention relateswill recognize various alternative designs and embodiments forpracticing the invention within the scope of the appended claims.

1. An active material actuator assembly comprising: a movable member:multiple active material components operatively connected to saidmovable member, each selectively activatable for moving said movablemember; and wherein movement of said movable member via activation of afirst of said active material components triggers activation of a secondof said active material components to further move said movable member.2. The active material actuator assembly of claim 1, further comprising:a first activation mechanism operatively connected to said first activematerial component; wherein an activation input to said first activematerial actuation mechanism causes activation of said first activematerial component to actuate said first active material component; anda second activation mechanism operatively connected to said secondactive material component; and wherein movement of said movable membervia actuation of said first active material component causes anactivation input to said second active activation mechanism to therebyactivate said second active material component.
 3. The active materialactuator assembly of claim 2, wherein said movable member is a shaftrotatable about a center axis, and further comprising: a cam lobe havinga cam surface operatively connected for rotation with said shaft; anextension member extending from said shaft offset from and substantiallyparallel with said center axis; wherein each of said active materialcomponents is operatively connected to said extension member; multiplesliding elements each having one of said active material componentsoperatively connected thereto; a base member having multiple slotstherein; and wherein a portion of each of said sliding elements isslidable within a respective one of said slots toward or away from saidcenter axis due to contact with said cam surface as said cam loberotates.
 4. The active material actuator assembly of claim 3, whereinsaid active material components extend in a substantially commondirection for attachment to said base member to increase compactness ofsaid active material actuator assembly.
 5. The active material actuatorassembly of claim 3, wherein one of said sliding elements is operativelyconnected with said second active material component; and wherein saidone of said sliding elements slides toward said center axis in one ofsaid slots as said second active material component is actuated tothereby minimize resetting of said first active material componentduring actuation of said second active material component.
 6. The activematerial actuator assembly of claim 3, wherein said first and secondactivation mechanisms are electrical contact members each on arespective circumferential surface of a different one of said slidingelements; and wherein said cam surface has an electrical contact memberextending partially therearound and axially positioned to be in contactwith said electrical contact strips on said sliding elements as said camlobe rotates such that said active material components are activatablein sequential order in a given rotational direction.
 7. The activematerial assembly of claim 2, wherein said movable member is a firstmovable member, and further comprising: a second movable member; a fixedmember; an anchor member; a base member; wherein said first movablemember, said second movable member, said fixed member and said anchormember are aligned on said base member in respective order; wherein saidfirst active material component connects said first movable member tosaid anchor member; wherein said second active material componentconnects said second active material member to said anchor member;wherein said first and second activation mechanisms are first and secondelectrical contact members offset from one another on said base member;wherein each of said movable members has an electrical contact memberthereon positioned to be electrically communicable with a respective oneof said electrical contact members on said base member; and whereinmovement of said first movable member via powering of said firstelectrical contact member causes said contact member of said secondmovable member to contact said second contact member, thereby activatingsaid second active material component.
 8. The active material assemblyof claim 2, wherein said movable member is a first movable member, andfurther comprising: a second movable member; an anchor member; whereinsaid first active material component is connected to said anchor memberand to said second movable member; wherein said second active materialcomponent is connected to said second movable member and said firstmovable member; and wherein said first movable member is engaged withsaid second movable member such that said first movable member moveswith said second movable member due to actuation of said first activematerial component.
 9. An active material actuator assembly comprising:a movable member; multiple active material components operativelyconnected to said movable member and selectively activatable in arepeating series for sequential actuation for moving said movablemember; and wherein said active material components are configured suchthat a previously activated one of said active material components isnot substantially stretched by actuation of a currently activated activematerial component.
 10. The active material actuator assembly of claim9, wherein said movable member is a shaft rotatable about a center axis;and further comprising: a cam lobe having a cam surface connected forrotation with said shaft: an extension member extending from said shaftoffset from and substantially parallel with said center axis; whereineach of said active material components is operatively connected to saidextension member and is selectively activatable to actuate and therebyrotate said shaft; multiple sliding elements each having one of saidactive material components operatively connected thereto; a base memberhaving multiple slots therein; and wherein a portion of each of saidsliding elements is slidable within a respective one of said slotstoward and away from said center axis due to contact with said camsurface as said cam lobe rotates.
 11. An active material actuatorassembly comprising: a movable member; multiple active materialcomponents operatively connected to said 5 movable member andselectively activatable in a repeating series for sequential actuationfor moving said movable member; and wherein said active materialcomponents are configured such that a subsequently activated one of saidactive material components is at least partially reset by actuation of acurrently activated one of said active material components.
 12. Theactive material actuator assembly of claim 11, wherein said movablemember is a shaft rotatable about a center axis, and further comprising:a cam lobe having a cam surface connected for rotation with said shaft:an extension member extending from said shaft offset from andsubstantially parallel with said center axis; wherein each of saidactive material components is operatively connected to said extensionmember and is selectively activatable to actuate and thereby rotate saidshaft; multiple sliding elements each having one of said active materialcomponents operatively connected thereto; a base member having multipleslots therein; and wherein a portion of each of said sliding elements isslidable within a respective one of said slots toward and away from saidcenter axis due to contact with said cam surface as said cam loberotates.